Wednesday, August 20, 2008
By Guy McCarthy
It's been a while since a really hard rain in or above Mill Creek Canyon.
But you can always find evidence of previous floods here.
The rock-filled canyon is a cleft between two steep mountain ridges in southwest San Bernardino County, about 80 miles east of Los Angeles. Elevation at the location pictured is roughly 6,080 feet above sea level.
Looking east toward Galena Peak, elevation 9,324 feet, the San Gorgonio Wilderness rises on the left to the highest mountain spine in Southern California. The flat-back summit of San Gorgonio Mountain stands at 11,499 feet, according to the U.S. Geological Survey.
Galena Peak is named in Spanish for the mineral lead. Miners years ago gave this utilitarian name to several mountains across the Western states. This particular Galena Peak is the easternmost high point of Yucaipa Ridge on the right, which forms the south wall of Mill Creek Canyon.
Geologists who specialize in tectonics, plate movement, and active faults say Yucaipa Ridge is one of the fastest-rising ridges in Southern California, squeezed by the San Andreas on one side and by the Mill Creek Fault beneath the boulder-strewn alley seen here.
With steep walls composed of tectonically shattered rock and vast watersheds rising up to 5,000 vertical feet above this point, Mill Creek Canyon is prone to periodic events of radical erosion. When it rains hard on the slopes above, this canyon literally spews mud and boulders. The tree trunks in the foreground are weathered and smooth, in part from transport to this spot.
The photo was taken today, just east of Vivian Creek trailhead.